The present invention relates to a transmission fluid cooling system for an automotive vehicle, and specifically to a transmission-fluid cooling system equipped with both a water-cooled oil cooler and an air-cooled oil cooler connected in series to each other and capable of cooling working fluid circulating through a transmission oil pump, a hydraulic control circuit, and a lubrication circuit in the transmission.
As shown in FIG. 4, a transmission fluid cooling system 30 often uses both a water-cooled oil cooler 31 and an air-cooled oil cooler 32 fluidly connected in series to each other, for enhanced cooling performance. Water-cooled oil cooler 31 serves to remove heat from working fluid by the forced circulation of engine coolant. Air-cooled oil cooler 32 serves to cool the working fluid by close contact with a large volume of outside air. Oil coolers 31 and 32 are fluidly connected to a control valve 35 and a lubrication circuit 36 in an automatic transmission 33 via a hydraulic line 37. Control valve 35 is incorporated in a control valve body 34 included in a hydraulic control circuit laid out in an automatic transmission 33. An oil pump 38 is provided to pressurize and send working fluid through its outlet port into the hydraulic line. The working fluid discharged from oil pump 38 circulates through control valve 35, water-cooled oil cooler 31, air-cooled oil cooler 32, and lubrication circuit 36, in that order (see FIG. 4). The working-fluid pressure produced by oil pump 38 is called xe2x80x9cline pressurexe2x80x9d. In other words, the line pressure is created on the working fluid in a connection line 39 between the inlet port of control valve 35 and the outlet port of oil pump 38. A hydraulic pressure substantially proportional to and less than the line pressure is created on the working fluid in a hydraulic line 40 leading from the outlet port of control valve 35 to water-cooled oil cooler 31. Transmission fluid cooling system 30 also includes a bypass valve 41 and a relief valve 42. Bypass valve 41 is constructed as an oil-temperature sensing element equipped bypass valve. The oil-temperature sensing element incorporated in bypass valve 41 is able to sense working-fluid temperature. When a temperature value of the working-fluid temperature detected by the oil-temperature sensing element of bypass valve 41 is low, bypass valve 41 fully opens to permit the working fluid to circulate via the bypass valve through the oil passages in automatic transmission 33, bypassing both the water-cooled oil cooler 31 and air-cooled oil cooler 32. This enhances the engine warm-up performance and prevents overcooling of the working fluid. Pressure relief valve 42 is provided to prevent an excessive rise in the line pressure. When the line pressure exceeds a set pressure level of relief valve 42, the relief valve fully opens to permit the working fluid to circulate via water-cooled oil cooler 31 and relief valve 42 through the oil passages in automatic transmission 33, bypassing only the air-cooled oil cooler 32.
Referring now to FIG. 5, there is shown a diagram of opening and closing characteristics of bypass valve 41 and relief valve 42 for line pressure and working-fluid temperature. As can be seen from the characteristic diagram of FIG. 5, in the transmission fluid cooling system 30 of FIG. 4, there are four control mode areas A, B, C, and D. In the first control mode area A that the engine is cold and thus the working-fluid temperature is very low, bypass valve 41 opens in response to the temperature sensed by the oil-temperature sensing element built in bypass valve 41, and therefore the working fluid is permitted to flow via bypass valve 41 through the oil passages in automatic transmission 33, bypassing two oil coolers 31 and 32. In the area B that the working-fluid temperature rises to a certain extent while the line pressure does not yet reach a predetermined pressure level, bypass valve 41 is repeatedly opened and closed depending upon a temperature rise/fall of working-fluid temperature. In the area C that the working-fluid temperature rises to a certain extent while the line pressure exceeds the predetermined pressure level, relief valve 42 opens due to the line pressure above the predetermined pressure level. Thus, in the area C, the working fluid is permitted to flow via water-cooled oil cooler 31 and relief valve 42 through the oil passages in automatic transmission 33, bypassing only the air-cooled oil cooler 32. In the area D that the working-fluid temperature exceeds a preset temperature value, for example when the engine has been warmed up and approaches operating temperature, bypass valve 41 and relief valve 42 are both closed to permit working-fluid flow flowing through both the water-cooled oil cooler 31 and air-cooled oil cooler 32 so as to increase the cooling action. One such transmission-fluid cooling system has been disclosed in Japanese Patent Provisional Publication No. 2000-46156.
In the transmission fluid cooling system 30 as shown in FIGS. 4 and 5, there are some drawbacks. First, in the low working-fluid temperature area A of FIG. 5, bypass valve 41 fully opens regardless of the magnitude of line pressure. In this case, there is no flow through water-cooled oil cooler 31, in other words, the working fluid cannot be rapidly warmed by way of engine-coolant circulation. A viscosity of working fluid supplied to moving transmission parts (for example clutch plates, transmission input shaft, planetary-gear system, and various bushings and bearings) for lubrication tends to be high. This increases fuel consumption.
Second, in the medium working-fluid temperature, low line-pressure area B of FIG. 5, assuming that the working-fluid temperature is above the preset temperature value but not sufficiently high, bypass valve 41 closes to permit working-fluid flow through both the water-cooled oil cooler 31 and air-cooled oil cooler 32. In this case, owing to a comparatively high viscous resistance (in particular, a higher viscous resistance of working fluid flowing through air-cooled oil cooler 32) and low line pressure, and thereby prevents adequate working-fluid supply into the oil passages. This results in re-cooling of the working fluid.
Third, in the transmission fluid cooling system 30 as shown in FIGS. 4 and 5, bypass valve 41 is located outside of the control valve 35 of control valve body 34. Thus, a bypass oil passage tends to be lengthened and complicated. In such a case, apart of the oil passages is exposed to the outside air. If the outside air temperature is low, there is an increased tendency for the fluid-flow resistance of working fluid flowing through the oil passages to increase. Due to the increased fluid-flow resistance, it is impossible to attain adequate working-fluid supply needed for good lubrication.
Accordingly, it is an object of the invention to provide a cooling system for working fluid used in an automatic transmission of an automotive vehicle, which avoids the aforementioned disadvantages.
It is another object of the invention to provide a cooling system for working fluid used in an automatic transmission of an automotive vehicle equipped with a water-cooled oil cooler and an air-cooled oil cooler connected in series to each other, which ensures optimal switching between operative and inoperative modes of each of the water-cooled oil cooler and air-cooled oil cooler depending upon the magnitude of line pressure as well as working-fluid temperature, when the working-fluid temperature is low.
It is a further object of the invention to provide a cooling system for working fluid used in an automatic transmission of an automotive vehicle equipped with a water-cooled oil cooler and an air-cooled oil cooler connected in series to each other, which permits an operative mode of the water-cooled oil cooler and an inoperative mode of the air-cooled oil cooler when the working-fluid temperature is low and the magnitude of line pressure is low, and when the working-fluid temperature is medium.
It is a still further object of the invention to provide a cooling system for working fluid used in an automatic transmission of an automotive vehicle equipped with a water-cooled oil cooler and an air-cooled oil cooler connected in series to each other, which permits operative modes of both the water-cooled oil cooler and air-cooled oil cooler when the working-fluid temperature is high.
It is another object of the invention to provide a simple cooling system for working fluid used in an automatic transmission of an automotive vehicle equipped with a water-cooled oil cooler and an air-cooled oil cooler connected in series to each other, in which a bypass circuit containing a bypass valve associated with both the water-cooled oil cooler and air-cooled oil cooler is unaffected by the outside air temperature and additionally the bypass circuit is compactly constructed while minimizing the entire length of the bypass circuit.
In order to accomplish the aforementioned and other objects of the present invention, a cooling system for working fluid used in an automatic transmission of an automotive vehicle, comprises a water-cooled oil cooler and an air-cooled oil cooler connected in series to each other and both disposed in an oil cooler line for cooling the working fluid, an oil pump located in the automatic transmission and disposed in the oil cooler line for pressurizing and sending the working fluid into the oil cooler line, a hydraulic control circuit disposed downstream of the oil pump for regulating a line pressure produced by the oil pump, a lubrication circuit located in the automatic transmission for lubrication of moving transmission parts, a first bypass valve that opens to permit the working fluid to circulate via the first bypass valve through the oil pump, the hydraulic control circuit and the lubrication circuit, bypassing the water-cooled oil cooler and the air-cooled oil cooler, only when a working-fluid temperature is less than or equal to a predetermined temperature and the line pressure is greater than or equal to a predetermined pressure, and a second bypass valve that opens to permit the working fluid to circulate via the water-cooled oil cooler and the second bypass valve through the oil pump, the hydraulic control circuit and the lubrication circuit, bypassing only the air-cooled oil cooler, only when the working-fluid temperature is less than or equal to a preset temperature value.
According to another aspect of the invention, a cooling system for working fluid used in an automatic transmission of an automotive vehicle, comprises a water-cooled oil cooler and an air-cooled oil cooler connected in series to each other and both disposed in an oil cooler line for cooling the working fluid, an oil pump located in the automatic transmission and disposed in the oil cooler line for pressurizing and sending the working fluid into the oil cooler line, a hydraulic control circuit disposed downstream of the oil pump for regulating a line pressure produced by the oil pump, a lubrication circuit located in the automatic transmission for lubrication of moving transmission parts, a first bypass valve that opens in response to a working-fluid temperature as well as the line pressure, to permit the working fluid to circulate via the first bypass valve through the oil pump, the hydraulic control circuit and the lubrication circuit, bypassing the water-cooled oil cooler and the air-cooled oil cooler, and the first bypass valve being located within a control valve body included in the hydraulic control circuit.
According to a further aspect of the invention, a cooling system for working fluid used in an automatic transmission of an automotive vehicle, comprises a water-cooled oil cooler and an air-cooled oil cooler connected in series to each other and both disposed in an oil cooler line for cooling the working fluid, an oil pump located in the automatic transmission and disposed in the oil cooler line for pressurizing and sending the working fluid into the oil cooler line, a hydraulic control circuit disposed downstream of the oil pump for regulating a line pressure produced by the oil pump, a lubrication circuit located in the automatic transmission for lubrication of moving transmission parts, a first bypass valve that opens to permit the working fluid to circulate via the first bypass valve through the oil pump, the hydraulic control circuit and the lubrication circuit, bypassing the water-cooled oil cooler and the air-cooled oil cooler, only when a hydraulic pressure created on the working fluid in a portion of the oil cooler line leading from an outlet of the hydraulic control circuit to an upstream side of the water-cooled oil cooler and the air-cooled oil cooler exceeds a preset pressure level, and a second bypass valve that opens to permit the working fluid to circulate via the water-cooled oil cooler and the second bypass valve through the oil pump, the hydraulic control circuit and the lubrication circuit, bypassing only the air-cooled oil cooler, only when a working-fluid temperature is less than or equal to a preset temperature value.
According to a still further aspect of the invention, a cooling system for working fluid used in an automatic transmission of an automotive vehicle, comprises a water-cooled oil cooler and an air-cooled oil cooler connected in series to each other and both disposed in an oil cooler line for cooling the working fluid, an oil pump located in the automatic transmission and disposed in the oil cooler line for pressurizing and sending the working fluid into the oil cooler line, a hydraulic control circuit disposed downstream of the oil pump for regulating a line pressure produced by the oil pump, a lubrication circuit located in the automatic transmission for lubrication of moving transmission parts, a temperature sensor that detects a working-fluid temperature, a first bypass valve that permits the working fluid to circulate via the first bypass valve through the oil pump, the hydraulic control circuit and the lubrication circuit, bypassing the water-cooled oil cooler and the air-cooled oil cooler, a second bypass valve that permits the working fluid to circulate via the water-cooled oil cooler and the second bypass valve through the oil pump, the hydraulic control circuit and the lubrication circuit, bypassing only the air-cooled oil cooler, and a control unit configured to be connected electronically to the temperature sensor, and the first and second bypass valves, for automatically controlling opening and closing operations of each of the first and second bypass valves depending on the line pressure as well as the working-fluid temperature and for controlling the line pressure depending on a sensor signal from the temperature sensor, the control unit comprising a first bypass valve control section keeping the first bypass valve opened in a first control mode area that the working-fluid temperature is low and the line pressure is high, and a second bypass valve control section keeping the second bypass valve closed in a second control mode area that the working-fluid temperature is high.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.